Recently, thermoplastic elastomers which are soft materials having rubber elasticity, require no vulcanizing step, and are capable of molding and recycling similarly to thermoplastic resins have been widely used in the fields of automobile parts, electric appliance parts, wire covering, medical parts, footwear, sundries, etc.
Among the thermoplastic elastomers, polystyrene-based thermoplastic elastomers such as styrene-butadiene block polymers (SBS) and styrene-isoprene block polymers (SIS) which are block copolymers of aromatic vinyl compounds-conjugate diene compounds are rich in flexibility and have a good rubber elasticity at ordinary temperature, and thermoplastic elastomer compounds obtained from them are excellent in processability and have widely used as substitutes for vulcanized rubbers.
Moreover, elastomer compositions obtained by hydrogenating intramolecular double bonds of block copolymers of styrene and conjugate dienes in these elastomers have been further widely used as elastomers having improved thermal aging resistance (thermal stability) and weathering resistance.
However, the thermoplastic elastomer compositions using these hydrogenated block copolymers contain problems in rubbery properties such as oil resistance, heat and pressure deformation ratio (compression set), and rubber elasticity at a high temperature and, as those improving these points, there are proposed crosslinked compounds obtained by crosslinking compositions containing hydrogenated derivatives of the above block copolymers (for example, cf. Patent Documents 1 to 5).
Moreover, the crosslinked compositions of hydrogenated block copolymers disclosed in the above Patent documents contain a problem that compression set at a high temperature, particularly 100° C. is still insufficient and mechanical strength tends to decrease. Thus, it is current situation that a performance level required for applications of conventional vulcanized rubbers is not achieved. In addition, there are problems in view of molding that shape retention becomes worse owing to low melt tension at a high temperature in extrusion molding and a molding cycle is prolonged in injection molding.
Furthermore, attempts of blending these thermoplastic elastomers with resins each having a polar group, such as polyamide-based polymers, polyester-based polymers, or polyurethane-based polymers have been made. For example, there are proposed melt blends of thermoplastic polymers selected from hydrogenated SBS block copolymers, olefinic elastomers, diene-based elastomers, urethane-based elastomers, and plasticized polyvinyl chloride and polyester-based thermoplastic elastomers or polyether block amides (for example, cf. Patent Documents 6 and 7).
However, the compositions have a bad property balance between compression set and hardness and also have insufficient compatibility, so that they have a defect that flexural fatigue properties and abrasion resistance are bad.
In order to solve the problems, there are disclosed a composition excellent in flexibility, thermal resistance and chemical resistance and having an improved compatibility, which is obtained by adding a modified polystyrene-based resin and/or modified polyolefin-based resin containing an epoxy group, an acid anhydride group or an oxazoline group to a composition containing a hydrogenated derivative of a block copolymer and a polyester-based resin (for example, cf. Patent Document 8) and a composition comprising a hydrogenated derivative of a block copolymer, a hydrogenated derivative containing a carboxylic acid group or its derivative group, and further a polyolefin resin and a thermoplastic polyester (for example, Patent Documents 9 and 10).
Moreover, there are disclosed a composition comprising a hydrogenated derivative of a block copolymer, a hydrogenated derivative containing a carboxylic acid group or its derivative group and further a thermoplastic polyurethane (for example, Patent Documents 11 to 14) and a composition comprising a hydrogenated derivative of a block copolymer, a hydrogenated derivative containing an epoxy group or its derivative group and further a thermoplastic polyurethane (for example, Patent Document 15). Furthermore, there is disclosed a technology of obtaining a molded article having a high peeling strength by bringing a vulcanized elastomer having a dicarboxylic acid anhydride group, such as a carboxylated polybutadiene, into direct contact with a thermoplastic elastomer having a polyamide block (for example, cf. Patent Document 16).
However, all the compositions also have defects that they are still insufficient in compatibility with thermoplastic elastomers, tensile properties at a high temperature, particularly 100° C., becomes worse, and further a property balance between compression set and hardness is bad. Moreover, depending on the alloy ratio with the thermoplastic elastomer, there are defects that moldability becomes worse, i.e., generation of surface layer peeling and flow mark in injection molding and generation of gum and rough surface in extrusion molding, and further low-molecular-weight components bleed out.
Furthermore, the present inventors have invented a thermoplastic resin composition of a resin having a polar group and a thermoplastic elastomer composition comprising a hydrogenated product or the like of a block copolymer, an ester-based compound, an organic peroxide (for example, cf. Patent Document 17), a thermoplastic resin composition comprising a polyacetal resin and a thermoplastic elastomer comprising a hydrogenated product of a block copolymer, a rubber softener, an organic peroxide, and a liquid polybutadiene having a hydroxyl group at the terminal (for example, cf. Patent Document 18), and a thermoplastic elastomer composition excellent in compatibility with a resin having a polar group obtained by graft polymerization of an elastomer with a monomer by blending an elastomer mixture of two kinds of hydrogenated block copolymers having different hydrogenation ratios, i.e., a hydrogenated block copolymer having a high hydrogenation rate and a hydrogenated block copolymer having a low hydrogenation rate, in a specific ratio with a rubber softener, an organic peroxide, a liquid polybutadiene having a hydroxyl group at the terminal, and optionally, various monomers (cf. Patent Document 19), but there arise a problem of occurrence of troubles that a large amount of gas generates during the molding depending on molding conditions and thus working environment becomes worse as well as bubbles tend to generate inside the molded articles in some cases.
Patent Document 1: JP 59-6236 A
Patent Document 2: JP 63-57662 A
Patent Document 3: JP 3-49927 B
Patent Document 4: JP 3-11291 B
Patent Document 5: JP 6-13628 B
Patent Document 6: JP 1-139241 A
Patent Document 7: JP 3-100045 A
Patent Document 8: JP 5-214209 A
Patent Document 9: JP 5-75016 B
Patent Document 10: JP 1-230660 A
Patent Document 11: JP 3-234745 A
Patent Document 12: JP 3-234755 A
Patent Document 13: JP 5-171003 A
Patent Document 14: JP 7-126474 A
Patent Document 15: JP 2-97554 A
Patent Document 16: JP 6-238827 A
Patent Document 17: JP 2003-20382 A
Patent Document 18: JP 2003-268193 A
Patent Document 19: JP 2003-286384 A